JP5911106B2 - Magnetic random access memory - Google Patents

Description

  The present invention relates to a magnetic random access memory (MRAM). In particular, the present invention relates to an MRAM including a memory cell and a reference cell.

  MRAM is a promising nonvolatile memory from the viewpoint of high integration and high-speed operation. In the MRAM, a magnetoresistive element exhibiting a “magnetoresistance effect” such as a TMR (Tunnel Magneto Resistance) effect is used. In the magnetoresistive element, for example, a magnetic tunnel junction (MTJ) in which a tunnel barrier layer is sandwiched between two ferromagnetic layers is formed. The two ferromagnetic layers include a magnetization fixed layer (pinned layer) whose magnetization direction is fixed and a magnetization free layer (free layer) whose magnetization direction can be reversed.

  The MTJ resistance value (R + ΔR) when the magnetization direction of the magnetization fixed layer and the magnetization free layer is “anti-parallel” is larger than the resistance value (R) when they are “parallel” due to the magnetoresistance effect. It is known to be. The MRAM uses this MTJ as a memory cell and stores data in a nonvolatile manner by utilizing the change in the resistance value. For example, the antiparallel state is associated with data “1”, and the parallel state is associated with data “0”. Data is written to the memory cell by reversing the magnetization direction of the magnetization free layer.

  A typical data writing method is a “magnetic field writing method” in which a magnetic field in a desired direction is applied to the magnetization free layer. In this case, a write wiring is provided in the vicinity of the MTJ, and a write current is passed through the write wiring. A write magnetic field induced by the write current is applied to the magnetization free layer, and the magnetization direction of the magnetization free layer is reversed according to the direction of the write magnetic field.

  In recent years, a “spin transfer method” has been proposed as a write method that can suppress an increase in write current accompanying the miniaturization of memory cells (see Patent Document 1 and Non-Patent Document 1). According to the spin injection method, a spin-polarized current is injected between the magnetization free layer and the magnetization fixed layer, and the magnetization free layer is caused by a direct interaction between the spin and magnetic moment of conduction electrons. Is reversed (Spin Transfer Magnetization Switching). Non-Patent Document 2 demonstrates spin injection magnetization reversal at a write current of 0.2 mA. Non-Patent Document 3 reports that the write current can be further reduced by using a perpendicular magnetization film having perpendicular magnetic anisotropy.

  Furthermore, Patent Document 2 and Patent Document 3 propose a “domain wall motion method” that applies spin injection magnetization reversal. According to the domain wall motion method, the magnetization free layer includes a magnetization switching region facing the magnetization fixed layer, and a magnetization fixed region provided on both sides of the magnetization switching region. A domain wall is formed between the magnetization switching region and the magnetization fixed region in the magnetization free layer. When writing data, a write current flows in the in-plane direction in the magnetization free layer, and the magnetization direction of the magnetization switching region is reversed by spin injection. This corresponds to the movement of the domain wall from one end to the other end of the magnetization switching region (Current-Driven Domain Wall Motion). That is, the domain wall moves in the magnetization free layer, and the resistance value of the MTJ, that is, the recording data changes depending on the position of the domain wall. In this sense, the domain wall motion type magnetization free layer may be referred to as a domain wall motion layer or a magnetization recording layer. Non-Patent Document 4 reports that current-driven domain wall motion is possible with a write current of about 0.05 mA in the case of a perpendicular magnetization film.

Japanese Patent Laid-Open No. 2005-93488 JP 2005-191032 A International Publication WO / 2007/020823

J. C. Slonczewski, Current-driven excitation of magnetic multilayers, Journal of Magnetism and Magnetic Materials, 159, L1-L7, 1996. T. Kawahara et al., 2Mb Spin-Transfer TorqueRAM (SPRAM) with Bit-by-Bit Bidirectional Current Write and Parallelizing-Direction Current Read, 2007 IEEE International Solid-State Circuits Conference, Session 26, 26.5. M. Nakayama et al., Spin transfer switchingin TbCoFe / CoFeB / MgO / CoFeB / TbCoFe magnetoresistive tunneling junctions withperpendicular magnetic anisotropy, 52nd Magnetism and Magnetic MaterialsConference, November 2007, BB-09. S. Fukami et al, Micromagnetic analysis of current driven domain wall motion in nano-strips with perpendicular magneticanisotropy, 52nd Magnetism and Magnetic Materials Conference, November 2007, FE-06.

The inventor of the present application paid attention to the following points.
FIG. 1 schematically shows a configuration of a general MRAM. The memory cell array 2 of the MRAM 1 has a plurality of cells arranged in a matrix. More specifically, the cell includes a memory cell MC for data recording and reference cells RC0 and RC1 that are referred to for generating a reference level when reading data. The memory cell MC and the reference cells RC0 and RC1 have magnetoresistive elements having the same structure.

  Data “0” or data “1” is stored in the memory cell MC. The resistance value of the magnetoresistive element of the memory cell MC is R0 when the data is “0”, and R1 when the data is “1”. The reference cell RC0 is set to data “0”, and the resistance value of the magnetoresistive element is R0. On the other hand, the reference cell RC1 is set to data “1”, and the resistance value of the magnetoresistive element is R1. Such setting of the reference cells RC0 and RC1 is performed by a method similar to that for writing data to the memory cell MC, and a dedicated set controller 4 is provided for this purpose.

  At the time of data reading, a read current is supplied to the reference cells RC0 and RC1 in addition to the memory cell MC to be read. The read circuit 3 generates a read level corresponding to the recording data of the memory cell MC based on the read current flowing through the memory cell MC. Further, the read circuit 3 generates a reference level corresponding to an intermediate resistance value between the resistance values R0 and R1 based on the read current flowing through each of the reference cells RC0 and RC1. Then, the read circuit 3 determines the recording data of the memory cell MC by comparing the read level with the reference level.

  As described above, when reading data from the MRAM 1, two types of reference cells RC0 and RC1 in which complementary data are recorded are used. Therefore, it is necessary to write complementary data to each of the reference cells RC0 and RC1 using the set controller 4 after the circuit of the MRAM 1 is manufactured. Such an initial setting process causes an increase in manufacturing time and manufacturing cost. In addition, providing the initial setting controller 4 increases the area of the MRAM 1.

  One object of the present invention is to provide a technique that eliminates the need for initial setting of a reference cell in an MRAM.

  In a first aspect of the present invention, a magnetic random access memory is provided. The magnetic random access memory includes a memory cell and a reference cell that is referenced to generate a reference level when reading data. The memory cell includes a first magnetoresistive element whose resistance value switches between a first value and a second value. On the other hand, the reference cell includes a second magnetoresistive element whose resistance value is fixed to a third value between the first value and the second value.

  In a second aspect of the present invention, a magnetic random access memory is provided. The magnetic random access memory includes a memory cell including a first magnetoresistive element and a reference cell including a second magnetoresistive element. The first magnetoresistive element includes a first magnetization fixed layer having a fixed magnetization direction, a first magnetization free layer including at least a magnetization switching region in which the magnetization direction is parallel or antiparallel to the magnetization direction of the first magnetization fixed layer, And a first magnetization fixed layer and a first nonmagnetic layer sandwiched between the magnetization reversal regions. On the other hand, the second magnetoresistive element is fixed in a second magnetization free layer including at least a magnetization region in which the direction of magnetic anisotropy is parallel to the first direction, and in a second direction in which the magnetization direction is orthogonal to the first direction. A second magnetization fixed layer; and a second nonmagnetic layer sandwiched between the second magnetization fixed layer and the magnetization region. The first magnetization fixed layer, the first magnetization free layer, the second magnetization fixed layer, and the second magnetization free layer have in-plane magnetic anisotropy.

  In a third aspect of the present invention, a magnetic random access memory is provided. The magnetic random access memory includes a memory cell including a first magnetoresistive element and a reference cell including a second magnetoresistive element. The first magnetoresistive element includes a first magnetization fixed layer having a fixed magnetization direction, a first magnetization free layer in which a domain wall moves, and a first nonmagnetic layer sandwiched between the first magnetization fixed layer and the first magnetization free layer. And having a layer. On the other hand, the second magnetoresistive element includes a second magnetization free layer having a domain wall formed at a predetermined position, a second magnetization fixed layer whose magnetization direction is fixed and overlapping the predetermined position, and a second magnetization fixed layer And a second nonmagnetic layer sandwiched between the second magnetization free layers.

  According to the present invention, the magnetoresistive element of the reference cell has a different structure from the magnetoresistive element of the memory cell. The resistance value of the magnetoresistive element of the reference cell is fixed at an intermediate level between data “0” and data “1”. Therefore, two types of reference cells in which complementary data are recorded are unnecessary, and initial setting of the reference cells is also unnecessary. As a result, the manufacturing time is shortened and the manufacturing cost is reduced. Further, since an initial setting controller is not necessary, the area of the MRAM is reduced.

FIG. 1 is a schematic diagram showing a configuration of a general MRAM. FIG. 2 is a schematic diagram showing the configuration of the MRAM according to the embodiment of the present invention. FIG. 3 shows an example of the structure of the memory cell and the reference cell according to the first embodiment of the present invention. FIG. 4 shows another example of the structure of the memory cell and the reference cell according to the first embodiment of the present invention. FIG. 5 shows a case where the first embodiment is applied to a magnetic field writing type. FIG. 6 shows a case where the first embodiment is applied to a spin injection type. FIG. 7 shows the structure of the memory cell and the reference cell when the first embodiment is applied to the domain wall motion type. FIG. 8 shows data writing in the domain wall motion type. FIG. 9 shows a modification of the memory cell and the reference cell when the first embodiment is applied to the domain wall motion type. FIG. 10 shows an example of the structure of the memory cell and the reference cell according to the second embodiment of the present invention. FIG. 11 shows another example of the structure of the memory cell and the reference cell according to the second embodiment of the present invention. FIG. 12 shows a case where the second embodiment is applied to the spin injection type. FIG. 13 shows an example of the structure of the memory cell and the reference cell when the second embodiment is applied to the domain wall motion type. FIG. 14 shows another example of the structure of the memory cell and the reference cell when the second embodiment is applied to the domain wall motion type. FIG. 15 shows an example of the planar shape of the memory cell and the reference cell in the second embodiment. FIG. 16 shows another example of the planar shape of the memory cell and the reference cell in the second embodiment. FIG. 17 shows data writing in the domain wall motion type. FIG. 18 shows an example of a cross-sectional structure of a memory cell and a reference cell according to the third embodiment of the present invention. FIG. 19 shows another example of the cross-sectional structures of the memory cell and the reference cell according to the third embodiment of the present invention. FIG. 20 shows an example of the planar shape of the memory cell in the third embodiment. FIG. 21 shows another example of the planar shape of the memory cell in the third embodiment. FIG. 22 shows an example of the planar shape of the reference cell in the third embodiment. FIG. 23 shows another example of the planar shape of the reference cell in the third embodiment.

  An MRAM according to an embodiment of the present invention will be described with reference to the accompanying drawings.

  FIG. 2 schematically shows a configuration of the MRAM 10 according to the embodiment of the present invention. The memory cell array 20 of the MRAM 10 has a plurality of cells arranged in a matrix. More specifically, the cell includes a memory cell MC for data recording and a reference cell RC that is referred to for generating a reference level when data is read.

  Data “0” or data “1” is stored in the memory cell MC. The memory cell MC includes a first magnetoresistive element, and the resistance value of the first magnetoresistive element is switched between R0 and R1 according to recording data. For example, in the case of data “0”, the resistance value of the first magnetoresistive element is R0, and in the case of data “1”, the resistance value is R1 larger than R0. On the other hand, the reference cell RC includes a second magnetoresistive element having a structure different from that of the first magnetoresistive element. The resistance value of the second magnetoresistive element is fixed to an intermediate value between R0 and R1 (hereinafter referred to as “R0.5”). That is, the second magnetoresistive element is formed in advance so that its resistance value is R0.5 alone.

  When reading data, a read current is passed through the memory cell MC to be read and the reference cell RC. The read circuit 30 generates a read level corresponding to the recording data of the memory cell MC based on the read current flowing through the memory cell MC. Further, the read circuit 3 generates a reference level corresponding to the intermediate resistance value R0.5 based on the read current flowing through the reference cell RC. Then, the reading circuit 30 determines the recording data of the memory cell MC by comparing the reading level with the reference level.

  Thus, according to the present embodiment, one type of reference cell RC whose resistance value is fixed to R0.5 is used instead of two types of reference cells in which complementary data is recorded. The reference cell RC is formed in advance so that the resistance value becomes R0.5, and the initial setting process of the reference cell RC is not necessary. As a result, the manufacturing time is shortened and the manufacturing cost is reduced. In addition, since an initial setting controller is not required, the area of the MRAM 10 is reduced.

  Further, the read circuit 30 does not need to calculate the reference level corresponding to the intermediate resistance value between the resistance values R0 and R1 with reference to the two types of reference cells in which the complementary data is recorded. The reference level is obtained directly by referring to one type of reference cell RC whose resistance value is fixed at R0.5. Therefore, the circuit configuration is simplified and the area of the MRAM 10 is reduced.

  Further, in FIG. 1 described above, two rows are required to arrange each of the two types of reference cells RC0 and RC1. On the other hand, in FIG. 2, one row is sufficient for arranging one type of reference cell RC. Since the area for the reference cell is not required for one column, the area of the memory cell array is reduced. Particularly in the case of a small-scale array, the area reduction effect becomes remarkable.

  Compared with the MRAM 1 shown in FIG. 1, the MRAM 10 according to the present embodiment has improved compatibility with an SRAM (Static RAM). This is because in the SRAM, complementary data is not written into two types of reference cells, and the memory state is not determined by comparison with an intermediate value between R0 and R1.

  Not only the magnetoresistive element but also any element whose resistance value is fixed to R0.5 can be applied to the reference cell RC. For example, it is conceivable to form a polysilicon resistor having a resistance value of R0.5. However, it is preferable from the viewpoint of the manufacturing process that the memory cell MC and the reference cell RC include the same structure. Therefore, it is preferable that the magnetoresistive element is applied to the reference cell RC. Hereinafter, various examples for realizing a magnetoresistive element whose resistance value is fixed to R0.5 will be described in detail.

1. 1. First embodiment 1-1. Basic Configuration FIG. 3 shows the structure of the memory cell MC and the reference cell RC according to the first embodiment of the present invention.

The memory cell MC includes the first magnetoresistive element 100. The first magnetoresistive element 100 includes a magnetization fixed layer 110, a tunnel barrier layer 120, and a magnetization free layer 130. The magnetization fixed layer 110 and the magnetization free layer 130 are ferromagnetic layers, and materials thereof include Fe, Co, and Ni. On the other hand, the tunnel barrier layer 120 is a nonmagnetic layer, and is a thin insulating film such as an Al ₂ O ₃ film or an MgO film. The tunnel barrier layer 120 is sandwiched between the magnetization fixed layer 110 and the magnetization free layer 130, and the MTJ is formed by the magnetization fixed layer 110, the tunnel barrier layer 120, and the magnetization free layer 130.

  The magnetization fixed layer 110 and the magnetization free layer 130 have in-plane magnetic anisotropy. Among these, the magnetization direction of the magnetization fixed layer 110 is fixed in one direction in the plane. For example, in FIG. 3, the magnetization direction of the magnetization fixed layer 110 is fixed in the + Y direction. Such a magnetization direction can be fixed, for example, by making an antiferromagnetic layer adjacent to the magnetization fixed layer 110. In addition, a laminated film (laminated ferri-coupled film) whose magnetizations are antiparallel coupled can be applied to the magnetization fixed layer 110. On the other hand, the magnetization direction of the magnetization free layer 130 (magnetization switching region) is reversible, and is parallel or antiparallel to the magnetization direction of the magnetization fixed layer 110. In FIG. 3, the magnetization easy axis of the magnetization free layer 130 is parallel to the Y direction, and the magnetization direction of the magnetization free layer 130 can be the + Y direction or the −Y direction. In particular, in FIG. 3, the planar shape of the magnetization free layer 130 is an ellipse, and the major axis of the ellipse is along the Y direction.

  When the magnetization direction of the magnetization free layer 130 is the + Y direction, that is, when the magnetization directions of the magnetization fixed layer 110 and the magnetization free layer 130 are parallel, the resistance value of the first magnetoresistance element 100 is “R0”. On the other hand, when the magnetization direction of the magnetization free layer 130 is the −Y direction, that is, when the magnetization directions of the magnetization fixed layer 110 and the magnetization free layer 130 are antiparallel, the resistance value of the first magnetoresistive element 100 is “R0”. Large “R1”. For example, the resistance value “R0” is associated with data “0”, and the resistance value “R1” is associated with data “1”.

On the other hand, the reference cell RC includes a second magnetoresistive element 150 different from the first magnetoresistive element 100. The second magnetoresistive element 150 includes a magnetization fixed layer 160, a tunnel barrier layer 170, and a magnetization free layer 180. The magnetization fixed layer 160 and the magnetization free layer 180 are ferromagnetic layers, and materials thereof include Fe, Co, and Ni. On the other hand, the tunnel barrier layer 170 is a nonmagnetic layer, and is a thin insulating film such as an Al ₂ O ₃ film or an MgO film. The tunnel barrier layer 170 is sandwiched between the magnetization fixed layer 160 and the magnetization free layer 180, and the MTJ is formed by the magnetization fixed layer 160, the tunnel barrier layer 170, and the magnetization free layer 180.

  The magnetization fixed layer 160 and the magnetization free layer 180 have in-plane magnetic anisotropy. Among these, the magnetization direction of the magnetization fixed layer 160 is fixed in one direction in the plane. For example, in FIG. 3, the magnetization direction of the magnetization fixed layer 160 is fixed in the + Y ′ direction. Such a magnetization direction can be fixed as in the case of the magnetization fixed layer 110 of the first magnetoresistive element 100.

  According to the present embodiment, the easy axis of magnetization free layer 180 (magnetization region) is orthogonal to the magnetization direction of magnetization fixed layer 160. In the example shown in FIG. 3, the easy axis of magnetization free layer 180 is parallel to the X ′ direction. In particular, in FIG. 3, the planar shape of the magnetization free layer 180 is an ellipse, and the major axis of the ellipse is along the X ′ direction. As a result, the magnetization direction of the magnetization free layer 180 is parallel to the X ′ direction and orthogonal to the magnetization direction of the magnetization fixed layer 160. Therefore, the resistance value of the second magnetoresistive element 150 is an intermediate value “R0.5” between R0 and R1. Thus, the magnetization free layer 180 is formed so that the easy axis of magnetization is orthogonal to the magnetization direction of the magnetization fixed layer 160. That is, the second magnetoresistive element 150 is formed in advance so that the resistance value is R0.5.

  A second magnetoresistive element 150 as shown in FIG. 4 is also possible. In the example of FIG. 4, the magnetization easy axis of the magnetization free layer 180 is parallel to the Y ′ direction, and the magnetization direction of the magnetization fixed layer 160 is fixed in the + X ′ direction. Even in this case, the magnetization direction of the magnetization free layer 180 and the magnetization direction of the magnetization fixed layer 160 are orthogonal, and R0.5 is realized.

  The XYZ coordinate system of the first magnetoresistive element and the X′-Y′-Z ′ coordinate system of the second magnetoresistive element may be the same or different. That is, the X axis, Y axis, and Z axis may or may not be parallel to the X ′ axis, Y ′ axis, and Z ′ axis, respectively. For example, the X axis may be parallel to the Y ′ axis, the Y axis may be antiparallel to the X ′ axis, and the Z axis may be parallel to the Z ′ axis. This also applies to embodiments described later.

  In the example shown in FIGS. 3 and 4, each layer of the first magnetoresistive element 100 and each layer of the second magnetoresistive element 150 are preferably formed in the same layer. Specifically, the magnetization fixed layer 110 and the magnetization fixed layer 160 are formed in the same layer, the tunnel barrier layer 120 and the tunnel barrier layer 170 are formed in the same layer, and the magnetization free layer 130 and the magnetization free layer 180 are formed in the same layer. It is formed. In this case, it is preferable that the Z-axis and the Z′-axis are parallel.

  When data is read, a read current is passed through each MTJ. As for the memory cell MC, a read current flows between the magnetization fixed layer 110 and the magnetization free layer 130. As a result, a read level corresponding to the recording data (R0 or R1) is generated. With respect to the reference cell RC, a read current flows between the magnetization fixed layer 160 and the magnetization free layer 180. Thereby, the reference level according to R0.5 is generated. By comparing the read level with the reference level, the recording data of the memory cell MC is determined.

  In the present embodiment, the following can be considered as a method of writing data to the memory cell MC.

1-2. Magnetic Field Writing Type FIG. 5 shows a case where the present embodiment is applied to a magnetic field writing type. In the case of the magnetic field writing type, the write wiring 140 is provided in the vicinity of the first magnetoresistive element 100 of the memory cell MC. At the time of data writing, a write current flows through the write wiring 140 and a magnetic field generated by the write current is applied to the magnetization free layer 130. The magnetic field applied to the magnetization free layer 130 includes a component parallel or antiparallel to the magnetization direction of the magnetization fixed layer 110.

  In the example of FIG. 5, the magnetization direction of the magnetization fixed layer 110 is fixed in the + Y direction. A write wiring 140 extending in the X direction is provided above the first magnetoresistive element 100, and a write current flows in the + X direction or the -X direction depending on the write data. Specifically, when data “1” is written, the first write current IW1 flows in the −X direction, and a magnetic field in the −Y direction is applied to the magnetization free layer 130. As a result, the magnetization direction of the magnetization free layer 130 is oriented in the −Y direction. On the other hand, when data “0” is written, the second write current IW2 flows in the + X direction, and a magnetic field in the + Y direction is applied to the magnetization free layer 130. As a result, the magnetization direction of the magnetization free layer 130 is directed to the + Y direction.

1-3. Spin Injection Type FIG. 6 shows a case where the first embodiment is applied to a spin injection type. In the case of the spin injection type, a write current at the time of data writing is also passed through the MTJ. That is, the write current flows between the magnetization fixed layer 110 and the magnetization free layer 130 through the tunnel barrier layer 120.

  In the example of FIG. 6, the magnetization direction of the magnetization fixed layer 110 is fixed in the + Y direction. The terminals T110 and T130 are electrically connected to the magnetization fixed layer 110 and the magnetization free layer 130, respectively. When data “1” is written, the first write current IW1 flows from the terminal T110 to the terminal T130. In this case, electrons having the same spin state as the magnetization fixed layer 110 move from the magnetization free layer 130 to the magnetization fixed layer 110. The magnetization direction of the magnetization free layer 130 is reversed to the −Y direction by spin transfer. On the other hand, when data “0” is written, the second write current IW2 flows from the terminal T130 to the terminal T110. In this case, electrons having the same spin state as the magnetization fixed layer 110 move from the magnetization fixed layer 110 to the magnetization free layer 130. The magnetization direction of the magnetization free layer 130 is reversed in the + Y direction by spin transfer.

1-4. FIG. 7 shows the structure of the memory cell MC and the reference cell RC when the first embodiment is applied to the domain wall motion type. In the domain wall motion type, a domain wall is formed in the magnetization free layer, and the domain wall moves in accordance with the write data.

  In the memory cell MC, the magnetization free layer 130 of the first magnetoresistive element 100 connects the first magnetization fixed region 131, the second magnetization fixed region 132, and the first magnetization fixed region 131 and the second magnetization fixed region 132. The magnetization switching region 133 is included. The first magnetization fixed region 131 is connected to the boundary B1 of the magnetization switching region 133, and the second magnetization fixed region 132 is connected to the boundary B2 of the magnetization switching region 133. In FIG. 7, the first magnetization fixed region 131, the second magnetization fixed region 132, and the magnetization switching region 133 are formed in a straight line. A notch 134 is formed adjacent to the boundary B1, and a notch 135 is formed adjacent to the boundary B2.

  The magnetization fixed layer 110 overlaps the magnetization switching region 133 in the magnetization free layer 130, and an MTJ is formed by the magnetization fixed layer 110, the tunnel barrier layer 120, and the magnetization switching region 133. In the example of FIG. 7, the magnetization direction of the magnetization fixed layer 110 is fixed in the + X direction.

  In the magnetization free layer 130, the magnetization direction of the magnetization switching region 133 can be reversed, and is parallel or antiparallel to the magnetization direction of the magnetization fixed layer 110. In FIG. 7, the magnetization easy axis of the magnetization switching region 133 is parallel to the X direction, and the magnetization direction of the magnetization switching region 133 can be the + X direction or the −X direction. On the other hand, the magnetization directions of the first magnetization fixed region 131 and the second magnetization fixed region 132 are both fixed to the direction toward the magnetization switching region 133 or away from the magnetization switching region 133. In the example of FIG. 7, the magnetization direction of the first magnetization fixed region 131 is fixed in the + X direction toward the magnetization switching region 133 (boundary B1), and the magnetization direction of the second magnetization fixed region 132 is the magnetization switching region 133 (boundary). It is fixed in the -X direction toward B2). That is, the magnetizations of the first magnetization fixed region 131 and the second magnetization fixed region 132 are fixed in opposite directions. The magnetization can be fixed by magnetostatic coupling or exchange coupling.

  When the magnetization direction of the magnetization switching region 133 is the + X direction, a domain wall is formed at the boundary B2. At this time, the magnetization directions of the magnetization switching region 133 and the magnetization fixed layer 110 are parallel, and the resistance value of the first magnetoresistance element 100 is “R0”. That is, the state where the domain wall is located at the boundary B2 corresponds to the data “0”. On the other hand, when the magnetization direction of the magnetization switching region 133 is the −X direction, a domain wall is formed at the boundary B1. At this time, the magnetization directions of the magnetization switching region 133 and the magnetization fixed layer 110 are antiparallel, and the resistance value of the first magnetoresistance element 100 is “R1”. That is, the state where the domain wall is located at the boundary B1 corresponds to the data “1”. The notches 134 and 135 are formed in order to stably fix the domain wall at the boundaries B1 and B2, respectively.

  The second magnetoresistive element 150 of the reference cell RC has substantially the same structure as the first magnetoresistive element 100. That is, the magnetization free layer 180 of the second magnetoresistive element 150 includes the first magnetization fixed region 181, the second magnetization fixed region 182, and the magnetization region 183 that connects the first magnetization fixed region 181 and the second magnetization fixed region 182. Is included. The first magnetization fixed region 181 is connected to the boundary B3 of the magnetization region 183, and the second magnetization fixed region 182 is connected to the boundary B4 of the magnetization region 183. In FIG. 7, the first magnetization fixed region 181, the second magnetization fixed region 182, and the magnetization region 183 are linearly formed. A notch 184 is formed adjacent to the boundary B3, and a notch 185 is formed adjacent to the boundary B4.

  In the magnetization free layer 180, the magnetization easy axis of the magnetization region 183 is parallel to the X ′ direction, and the magnetization direction of the magnetization region 183 is the + X ′ direction or the −X ′ direction. The magnetization directions of the first magnetization fixed region 181 and the second magnetization fixed region 182 are both fixed toward the magnetization region 183 or away from the magnetization region 183. In the example of FIG. 7, the magnetization direction of the first magnetization fixed region 181 is fixed in the + X ′ direction toward the magnetization region 183 (boundary B3), and the magnetization direction of the second magnetization fixed region 182 is the magnetization region 183 (boundary B4). It is fixed in the −X ′ direction toward That is, the magnetizations of the first magnetization fixed region 181 and the second magnetization fixed region 182 are fixed in opposite directions. The magnetization can be fixed by magnetostatic coupling or exchange coupling.

  The magnetization fixed layer 160 overlaps the magnetization region 183 in the magnetization free layer 180, and an MTJ is formed by the magnetization fixed layer 160, the tunnel barrier layer 170, and the magnetization region 183. The difference between the second magnetoresistive element 150 and the first magnetoresistive element 100 is the magnetization direction of the magnetization fixed layer. That is, in the second magnetoresistive element 150, the magnetization direction of the magnetization fixed layer 160 is fixed in a direction orthogonal to the easy magnetization axis of the magnetization region 183. In the example of FIG. 7, the magnetization direction of the magnetization fixed layer 160 is fixed in the + Y ′ direction. As a result, the resistance value of the second magnetoresistive element 150 becomes an intermediate value “R0.5” between R0 and R1.

  FIG. 8 shows data writing in the domain wall motion type. In the domain wall motion type, the write current flows in a plane in the magnetization free layer 130, not in the direction penetrating the MTJ. Therefore, the terminals T131 and T132 are electrically connected to the first magnetization fixed region 131 and the second magnetization fixed region 132 of the magnetization free layer 130, respectively.

  During a transition from data “0” to data “1”, the first write current IW1 flows from the terminal T131 to the terminal T132. In this case, electrons (spin electrons) are injected from the second magnetization fixed region 132 into the magnetization switching region 133. By spin transfer, the domain wall moves from the boundary B2 to the boundary B1 in accordance with the moving direction of the electrons, and the magnetization direction of the magnetization switching region 133 is reversed in the −X direction. On the other hand, at the time of transition from data “1” to data “0”, the second write current IW2 flows from the terminal T132 to the terminal T131. In this case, electrons (spin electrons) are injected from the first magnetization fixed region 131 into the magnetization switching region 133. By spin transfer, the domain wall moves from the boundary B1 to the boundary B2 in accordance with the moving direction of the electrons, and the magnetization direction of the magnetization switching region 133 is reversed in the + X direction. Thus, the write currents IW1 and IW2 flow in the magnetization free layer 130, and the domain wall in the magnetization free layer 130 moves between the boundary B1 and the boundary B2 (current-driven domain wall motion: Current-Driven Domain Wall Motion ).

  FIG. 9 shows a modification of the memory cell MC and the reference cell RC in the domain wall motion type. According to this modification, the first magnetization fixed region 131, the second magnetization fixed region 132, and the magnetization switching region 133 of the magnetization free layer 130 are formed in a U shape. Even in this case, the magnetization directions of the first magnetization fixed region 131 and the second magnetization fixed region 132 are both fixed in the direction toward the magnetization switching region 133 or away from the magnetization switching region 133. However, in the case of the U shape, the magnetization directions of the first magnetization fixed region 131 and the second magnetization fixed region 132 are the same. In the example of FIG. 9, the magnetization direction of the first magnetization fixed region 131 is fixed in the −Y direction toward the magnetization switching region 133 (boundary B <b> 1), and the magnetization direction of the second magnetization fixed region 132 is also the magnetization switching region 133 ( It is fixed in the -Y direction towards the boundary B2). The magnetization can be fixed not only by magnetostatic coupling or exchange coupling but also by shape magnetic anisotropy.

  The same applies to the reference cell RC. The first magnetization fixed region 181, the second magnetization fixed region 182, and the magnetization region 183 of the magnetization free layer 180 are formed in a U shape. Even in this case, the magnetization directions of the first magnetization fixed region 181 and the second magnetization fixed region 182 are both fixed toward the magnetization region 183 or away from the magnetization region 183. Others are the same as the example shown in FIG. Since the magnetization direction of the magnetization fixed layer 160 and the magnetization direction of the magnetization region 183 are orthogonal to each other, the resistance value of the second magnetoresistive element 150 is “R0.5”.

2. Second embodiment 2-1. Basic Configuration FIG. 10 shows the structure of a memory cell MC and a reference cell RC according to the second embodiment of the present invention. In the second embodiment, a perpendicular magnetization film having perpendicular magnetic anisotropy is used. The perpendicular magnetization film preferably includes at least one selected from Fe, Co, and Ni. Furthermore, perpendicular magnetic anisotropy can be stabilized by including Pt and Pd. In addition to this, B, C, N, O, Al, Si, P, Ti, V, Cr, Mn, Cu, Zn, Zr, Nb, Mo, Tc, Ru, Rh, Ag, Hf, Ta, W , Re, Os, Ir, Au, Sm and the like can be added so that desired magnetic properties can be expressed. An example of a suitable perpendicular magnetization film is a Co—Pt—Cr alloy.

  The memory cell MC includes a first magnetoresistive element 200. The first magnetoresistive element 200 includes a magnetization fixed layer 210, a tunnel barrier layer 220, and a magnetization free layer 230. The tunnel barrier layer 220 is sandwiched between the magnetization fixed layer 210 and the magnetization free layer 230, and the MTJ is formed by the magnetization fixed layer 210, the tunnel barrier layer 220, and the magnetization free layer 230.

  The magnetization fixed layer 210 and the magnetization free layer 230 have perpendicular magnetic anisotropy. Among these, the magnetization direction of the magnetization fixed layer 210 is fixed to one direction. On the other hand, the magnetization direction of the magnetization free layer 230 (magnetization reversal region) can be reversed, and is parallel or antiparallel to the magnetization direction of the magnetization fixed layer 210. For example, in FIG. 10, the magnetization direction of the magnetization fixed layer 210 is fixed in the + Z direction, and the magnetization direction of the magnetization free layer 230 can be the + Z direction or the −Z direction. When the magnetization direction of the magnetization free layer 230 is the + Z direction, that is, when the magnetization directions of the magnetization fixed layer 210 and the magnetization free layer 230 are parallel, the resistance value of the first magnetoresistive element 200 is “R0”. On the other hand, when the magnetization direction of the magnetization free layer 230 is the −Z direction, that is, when the magnetization directions of the magnetization fixed layer 210 and the magnetization free layer 230 are antiparallel, the resistance value of the first magnetoresistive element 200 is “R1”. is there.

  On the other hand, the reference cell RC includes a second magnetoresistive element 250 different from the first magnetoresistive element 200. The second magnetoresistive element 250 includes a magnetization fixed layer 260, a tunnel barrier layer 270, and a magnetization free layer 280. The tunnel barrier layer 270 is sandwiched between the magnetization fixed layer 260 and the magnetization free layer 280, and the MTJ is formed by the magnetization fixed layer 260, the tunnel barrier layer 270, and the magnetization free layer 280.

  The magnetization fixed layer 260 and the magnetization free layer 280 have perpendicular magnetic anisotropy. However, according to the present embodiment, the magnetization of either the magnetization fixed layer 260 or the magnetization free layer 280 is directed in the in-plane direction by some means. As some means, it is conceivable to reduce the perpendicular magnetic anisotropy by reducing the thickness of the perpendicular magnetization film. Alternatively, a ferromagnetic film or an antiferromagnetic film having in-plane magnetic anisotropy may be adjacent.

  For example, in FIG. 10, an in-plane magnetization film 290 (for example, an antiferromagnetic film) having in-plane magnetic anisotropy is formed adjacent to the magnetization free layer 280. The in-plane magnetization film 290 is antiferromagnetically or ferromagnetically coupled to the magnetization free layer 280. As a result, the magnetization of the magnetization free layer 280 (magnetization region) is directed in the in-plane direction. In the example of FIG. 10, the magnetization direction of the magnetization free layer 280 is the + X ′ direction. On the other hand, the magnetization direction of the magnetization fixed layer 260 is fixed in the + Z ′ direction. That is, in the second magnetoresistive element 250, the magnetization direction of the magnetization free layer 280 and the magnetization direction of the magnetization fixed layer 260 are orthogonal to each other. Therefore, the resistance value of the second magnetoresistive element 250 is an intermediate value “R0.5” between R0 and R1.

  In FIG. 11, an in-plane magnetization film 290 (for example, an antiferromagnetic film) having in-plane magnetic anisotropy is formed adjacent to the magnetization fixed layer 260. The in-plane magnetization film 290 is antiferromagnetically or ferromagnetically coupled to the magnetization fixed layer 260. As a result, the magnetization of the magnetization fixed layer 260 is directed in the in-plane direction. In the example of FIG. 11, the magnetization direction of the magnetization fixed layer 260 is the + X ′ direction. On the other hand, the magnetization direction of the magnetization free layer 280 is the −Z ′ direction. That is, in the second magnetoresistive element 250, the magnetization direction of the magnetization free layer 280 and the magnetization direction of the magnetization fixed layer 260 are orthogonal to each other. Therefore, the resistance value of the second magnetoresistive element 250 is an intermediate value “R0.5” between R0 and R1.

  In the example shown in FIGS. 10 and 11, each layer of the first magnetoresistive element 200 and each layer of the second magnetoresistive element 250 are preferably formed in the same layer. Specifically, the magnetization fixed layer 210 and the magnetization fixed layer 260 are formed in the same layer, the tunnel barrier layer 220 and the tunnel barrier layer 270 are formed in the same layer, and the magnetization free layer 230 and the magnetization free layer 280 are formed in the same layer. It is formed. In this case, it is preferable that the Z-axis and the Z′-axis are parallel.

  When data is read, a read current is passed through each MTJ. With respect to the memory cell MC, a read current flows between the magnetization fixed layer 210 and the magnetization free layer 230. As a result, a read level corresponding to the recording data (R0 or R1) is generated. Regarding the reference cell RC, a read current is passed between the magnetization fixed layer 260 and the magnetization free layer 280. Thereby, the reference level according to R0.5 is generated. By comparing the read level with the reference level, the recording data of the memory cell MC is determined.

  In the present embodiment, the following can be considered as a method of writing data to the memory cell MC.

2-2. Spin Injection Type FIG. 12 shows a case where the second embodiment is applied to a spin injection type. Terminals T210 and T230 are electrically connected to the magnetization fixed layer 210 and the magnetization free layer 230, respectively. When data “1” is written, the first write current IW1 flows from the terminal T210 to the terminal T230. In this case, electrons having the same spin state as the magnetization fixed layer 210 move from the magnetization free layer 230 to the magnetization fixed layer 210. The magnetization direction of the magnetization free layer 230 is reversed to the −Z direction by spin transfer. On the other hand, when data “0” is written, the second write current IW2 flows from the terminal T230 to the terminal T210. In this case, electrons having the same spin state as the magnetization fixed layer 210 move from the magnetization fixed layer 210 to the magnetization free layer 230. By spin transfer, the magnetization direction of the magnetization free layer 230 is reversed to the + Z direction.

2-3. FIG. 13 shows the structure of the memory cell MC and the reference cell RC when the second embodiment is applied to the domain wall motion type.

  In the memory cell MC, the magnetization free layer 230 of the first magnetoresistance element 200 connects the first magnetization fixed region 231, the second magnetization fixed region 232, and the first magnetization fixed region 231 and the second magnetization fixed region 232. The magnetization switching region 233 is included. The first magnetization fixed region 231 is connected to the boundary B1 of the magnetization switching region 233, and the second magnetization fixed region 232 is connected to the boundary B2 of the magnetization switching region 233. The magnetization fixed layer 210 overlaps with the magnetization switching region 233 in the magnetization free layer 230, and an MTJ is formed by the magnetization fixed layer 210, the tunnel barrier layer 220, and the magnetization switching region 233. In the example of FIG. 13, the magnetization direction of the magnetization fixed layer 210 is fixed in the + Z direction.

  In the magnetization free layer 230, the magnetization direction of the magnetization switching region 233 can be reversed, and is parallel or antiparallel to the magnetization direction of the magnetization fixed layer 210. On the other hand, the magnetization directions of the first magnetization fixed region 231 and the second magnetization fixed region 232 are fixed in opposite directions. In the example of FIG. 13, the magnetization direction of the first magnetization fixed region 231 is fixed in the + Z direction, and the magnetization direction of the second magnetization fixed region 232 is fixed in the −Z direction. When the magnetization direction of the magnetization switching region 233 is the + Z direction, a domain wall is formed at the boundary B2. At this time, the magnetization direction of the magnetization switching region 233 and the magnetization fixed layer 210 is parallel, and the resistance value of the first magnetoresistance element 200 is “R0”. On the other hand, when the magnetization direction of the magnetization switching region 233 is the −Z direction, a domain wall is formed at the boundary B1. At this time, the magnetization direction of the magnetization switching region 233 and the magnetization fixed layer 210 is antiparallel, and the resistance value of the first magnetoresistance element 200 is “R1”.

  In the reference cell RC, the magnetization free layer 280 of the second magnetoresistive element 250 connects the first magnetization fixed region 281, the second magnetization fixed region 282, and the first magnetization fixed region 281 and the second magnetization fixed region 282. A magnetized region 283 is included. The first magnetization fixed region 281 is connected to the boundary B3 of the magnetization region 283, and the second magnetization fixed region 282 is connected to the boundary B4 of the magnetization region 283. The magnetization fixed layer 260 overlaps the magnetization region 283 in the magnetization free layer 280, and the MTJ is formed by the magnetization fixed layer 260, the tunnel barrier layer 270, and the magnetization region 283.

  In FIG. 13, the in-plane magnetization film 290 is adjacent to at least the magnetization region 283 in the magnetization free layer 280 as in the case of FIG. 10 described above. As a result, at least the magnetization of the magnetization region 283 is directed in the in-plane direction. In the example of FIG. 13, the magnetization direction of the magnetization region 283 is the + X ′ direction. On the other hand, the magnetization direction of the magnetization fixed layer 260 is fixed in the + Z ′ direction. That is, in the second magnetoresistive element 250, the magnetization direction of the magnetization region 283 and the magnetization direction of the magnetization fixed layer 260 are orthogonal to each other. Therefore, the resistance value of the second magnetoresistive element 250 is “R0.5”.

  FIG. 14 shows another example. In FIG. 14, the in-plane magnetization film 290 is formed adjacent to the magnetization fixed layer 260 as in the case of FIG. As a result, the magnetization of the magnetization fixed layer 260 is directed in the in-plane direction. In the example of FIG. 14, the magnetization direction of the magnetization fixed layer 260 is the + X ′ direction. On the other hand, in the magnetization free layer 280, the magnetization direction of the magnetization region 283 is the + Z ′ direction or the −Z ′ direction. That is, in the second magnetoresistive element 250, the magnetization direction of the magnetization region 283 and the magnetization direction of the magnetization fixed layer 260 are orthogonal to each other. Therefore, the resistance value of the second magnetoresistive element 250 is “R0.5”. In FIG. 14, the magnetization directions of the first magnetization fixed region 281 and the second magnetization fixed region 282 may be fixed in opposite directions.

  15 and 16 show examples of the planar shape of the first magnetoresistive element 200 or the second magnetoresistive element 250. FIG. The magnetization free layer 230 (magnetization free layer 280) may be formed in a straight line shape as shown in FIG. 15, or may be formed in a U shape as shown in FIG.

  FIG. 17 shows data writing in the domain wall motion type. Terminals T231 and T232 are electrically connected to the first magnetization fixed region 231 and the second magnetization fixed region 232 of the magnetization free layer 230, respectively. At the time of transition from data “0” to data “1”, the first write current IW1 flows from the terminal T231 to the terminal T232. In this case, electrons are injected from the second magnetization fixed region 232 into the magnetization switching region 233. By spin transfer, the domain wall moves from the boundary B2 to the boundary B1, and the magnetization direction of the magnetization switching region 233 is reversed in the −Z direction. On the other hand, at the time of transition from data “1” to data “0”, the second write current IW2 flows from the terminal T232 to the terminal T231. In this case, electrons are injected from the first magnetization fixed region 231 into the magnetization switching region 233. Due to the spin transfer, the domain wall moves from the boundary B1 to the boundary B2, and the magnetization direction of the magnetization switching region 233 is reversed in the + Z direction. In this way, the write currents IW1 and IW2 flow in the magnetization free layer 230, and the domain wall in the magnetization free layer 230 moves between the boundary B1 and the boundary B2.

3. Third Embodiment A third embodiment of the present invention is applied to a domain wall motion type. As described in the foregoing embodiments, in the domain wall motion type, the domain wall moves in the magnetization free layer of the memory cell MC. The resistance value “R0” or “R1” is determined by the position of the domain wall. In the third embodiment, a domain wall is formed at a position where the resistance value is “R0.5” in the magnetization free layer of the reference cell RC.

  FIG. 18 shows an example of a cross-sectional structure of the memory cell MC and the reference cell RC according to the present embodiment. In the example shown in FIG. 18, an in-plane magnetization film having in-plane magnetic anisotropy is used.

  The memory cell MC includes a first magnetoresistive element 300. The first magnetoresistive element 300 includes a magnetization fixed layer 310, a tunnel barrier layer 320, and a magnetization free layer 330. The tunnel barrier layer 320 is sandwiched between the magnetization fixed layer 310 and the magnetization free layer 330.

  The magnetization free layer 330 includes a first magnetization fixed region 331, a second magnetization fixed region 332, and a magnetization switching region 333 that connects the first magnetization fixed region 331 and the second magnetization fixed region 332. The first magnetization fixed region 331 is connected to the boundary B1 of the magnetization switching region 333, and the second magnetization fixed region 332 is connected to the boundary B2 of the magnetization switching region 333. The magnetization fixed layer 310 overlaps with the magnetization switching region 333 in the magnetization free layer 330, and an MTJ is formed by the magnetization fixed layer 310, the tunnel barrier layer 320, and the magnetization switching region 333. In the example of FIG. 18, the magnetization direction of the magnetization fixed layer 310 is fixed in the + X direction.

  In the magnetization free layer 330, the magnetization direction of the magnetization switching region 333 can be reversed, and is parallel or antiparallel to the magnetization direction of the magnetization fixed layer 310. On the other hand, the magnetization directions of the first magnetization fixed region 331 and the second magnetization fixed region 332 are both fixed toward the magnetization switching region 333 or away from the magnetization switching region 333. The magnetization can be fixed by magnetostatic coupling or exchange coupling. In the example of FIG. 18, the magnetization direction of the first magnetization fixed region 331 is fixed in the direction toward the magnetization switching region 333 (boundary B1), and the magnetization direction of the second magnetization fixed region 332 is the magnetization switching region 333 (boundary B2). ) Is fixed in the direction toward. When the magnetization direction of the magnetization switching region 333 is the + X direction, a domain wall is formed at the boundary B2. At this time, the magnetization directions of the magnetization switching region 333 and the magnetization fixed layer 310 are parallel, and the resistance value of the first magnetoresistance element 300 is “R0”. On the other hand, when the magnetization direction of the magnetization switching region 333 is the −X direction, a domain wall is formed at the boundary B1. At this time, the magnetization directions of the magnetization switching region 333 and the magnetization fixed layer 310 are antiparallel, and the resistance value of the first magnetoresistance element 300 is “R1”.

  On the other hand, the reference cell RC includes a second magnetoresistive element 350 different from the first magnetoresistive element 300. The second magnetoresistive element 350 has a magnetization fixed layer 360, a tunnel barrier layer 370 and a magnetization free layer 380. The tunnel barrier layer 370 is sandwiched between the magnetization fixed layer 360 and the magnetization free layer 380, and the MTJ is formed by the magnetization fixed layer 360, the tunnel barrier layer 370, and the magnetization free layer 380.

  According to the present embodiment, the domain wall is formed at the predetermined position B3 in the magnetization free layer 380. More specifically, the magnetization free layer 380 includes a first magnetization fixed region 381 and a second magnetization fixed region 382 that are opposed to each other with the predetermined position B3 interposed therebetween. The magnetization directions of the first magnetization fixed region 381 and the second magnetization fixed region 382 are both fixed in the direction toward the position B3 or away from the position B3. As a result, a domain wall is formed at a position B3 that is a boundary between the first magnetization fixed region 381 and the second magnetization fixed region 382. In the example of FIG. 18, the magnetization directions of the first magnetization fixed region 381 and the second magnetization fixed region 382 are both fixed in the direction toward the position B3. The magnetization can be fixed by magnetostatic coupling or exchange coupling.

  The magnetization direction of the magnetization fixed layer 360 is fixed in one direction in the plane. For example, in FIG. 18, the magnetization direction of the magnetization fixed layer 360 is fixed in the + X ′ direction. Further, according to the present embodiment, the magnetization fixed layer 360 is formed so as to overlap the predetermined position B3 in the magnetization free layer 380. That is, the magnetization fixed layer 360 extends over both the first magnetization fixed region 381 and the second magnetization fixed region 382. In the example of FIG. 18, the magnetization direction of the magnetization fixed layer 360 is parallel to the magnetization direction of the first magnetization fixed region 381, while being antiparallel to the magnetization direction of the second magnetization fixed region 382. As a result, the resistance value of the second magnetoresistive element 350 is “R0.5”. In this way, “R0.5” is realized by forming the domain wall at a position overlapping the magnetization fixed layer 360 in the magnetization free layer 380.

  FIG. 19 shows another example of a cross-sectional structure of the memory cell MC and the reference cell RC according to the present embodiment. In the example shown in FIG. 19, a perpendicular magnetization film having perpendicular magnetic anisotropy is used.

  The magnetization state of the first magnetoresistive element 300 of the memory cell MC is as follows. The magnetization direction of the magnetization fixed layer 310 is fixed in the + Z direction. In the magnetization free layer 330, the magnetization direction of the magnetization switching region 333 can be reversed, and is parallel or antiparallel to the magnetization direction of the magnetization fixed layer 310. The magnetization directions of the first magnetization fixed region 331 and the second magnetization fixed region 332 are fixed in opposite directions. In the example of FIG. 19, the magnetization direction of the first magnetization fixed region 331 is fixed in the + Z direction, and the magnetization direction of the second magnetization fixed region 332 is fixed in the −Z direction. When the magnetization direction of the magnetization switching region 333 is the + Z direction, a domain wall is formed at the boundary B2. On the other hand, when the magnetization direction of the magnetization switching region 333 is the −Z direction, a domain wall is formed at the boundary B1.

  The magnetization state of the second magnetoresistive element 350 of the reference cell RC is as follows. The magnetization direction of the magnetization fixed layer 360 is fixed in the + Z ′ direction. In the magnetization free layer 380, the magnetization directions of the first magnetization fixed region 381 and the second magnetization fixed region 382 are fixed in opposite directions. In the example of FIG. 19, the magnetization direction of the first magnetization fixed region 381 is fixed in the + Z ′ direction, and the magnetization direction of the second magnetization fixed region 332 is fixed in the −Z ′ direction. As a result, a domain wall is formed at a position B3 that is a boundary between the first magnetization fixed region 381 and the second magnetization fixed region 382.

  Also in FIG. 19, the magnetization fixed layer 360 is formed so as to overlap with the domain wall position B <b> 3 in the magnetization free layer 380. Therefore, the resistance value of the second magnetoresistive element 350 is “R0.5”.

  In the example shown in FIGS. 18 and 19, it is preferable that each layer of the first magnetoresistive element 300 and each layer of the second magnetoresistive element 350 are formed in the same layer. Specifically, the magnetization fixed layer 310 and the magnetization fixed layer 360 are formed in the same layer, the tunnel barrier layer 320 and the tunnel barrier layer 370 are formed in the same layer, and the magnetization free layer 330 and the magnetization free layer 380 are formed in the same layer. It is formed. In this case, it is preferable that the Z-axis and the Z′-axis are parallel.

  When data is read, a read current is passed through each MTJ. With respect to the memory cell MC, a read current flows between the magnetization fixed layer 310 and the magnetization free layer 330. As a result, a read level corresponding to the recording data (R0 or R1) is generated. With respect to the reference cell RC, a read current flows between the magnetization fixed layer 360 and the magnetization free layer 380. Thereby, the reference level according to R0.5 is generated. By comparing the read level with the reference level, the recording data of the memory cell MC is determined.

  The method of writing data to the memory cell MC is the same as that described in the above embodiments. In the case of the example shown in FIG. 18, data writing is the same as the case of FIG. In the case of the example shown in FIG. 19, data writing is the same as the case of FIG.

  20 and 21 show examples of the planar shape of the first magnetoresistive element 300 of the memory cell MC shown in FIG. 18 or FIG. In FIG. 20, the magnetization free layer 330 is formed linearly. In this case, the magnetization directions of the first magnetization fixed region 331 and the second magnetization fixed region 332 are opposite to each other. In FIG. 21, the magnetization free layer 330 is formed in a U shape. When the magnetization free layer 330 is U-shaped and has in-plane magnetic anisotropy, the shape magnetic anisotropy can be used to fix the magnetization of the first magnetization fixed region 331 and the second magnetization fixed region 332. Is preferable.

  22 and 23 show examples of the planar shape of the second magnetoresistive element 350 of the reference cell RC shown in FIG. 18 or FIG. In FIG. 22, the magnetization free layer 380 is formed linearly. In this case, the magnetization directions of the first magnetization fixed region 381 and the second magnetization fixed region 382 are opposite to each other. A notch 384 is formed adjacent to the position B3 in order to stably keep the domain wall at the position B3. In FIG. 23, the first magnetization fixed region 381 and the second magnetization fixed region 382 of the magnetization free layer 380 are formed in a V shape. It is desirable that the first magnetization fixed region 381 and the second magnetization fixed region 382 are formed symmetrically with the boundary B3 interposed therebetween. When the magnetization free layer 380 is V-shaped and has in-plane magnetic anisotropy, the shape magnetic anisotropy can be used to fix the magnetization of the first magnetization fixed region 381 and the second magnetization fixed region 382. Is preferable.

  The embodiments of the present invention have been described above with reference to the accompanying drawings. However, the present invention is not limited to the above-described embodiments, and can be appropriately changed by those skilled in the art without departing from the scope of the invention.

MC memory cell RC reference cell 10 MRAM
DESCRIPTION OF SYMBOLS 20 Memory cell array 30 Read circuit 100,200,300 1st magnetoresistive element 110,210,310 Magnetization fixed layer 120,220,320 Tunnel barrier layer 130,230,330 Magnetization free layer 131,231,331 1st magnetization fixed area | region 132, 232, 332 Second magnetization fixed region 133, 233, 333 Magnetization reversal region 134, 135 Notch 140 Write wiring 150, 250, 350 Second magnetoresistive element 160, 260, 360 Magnetization fixed layer 170, 270, 370 Tunnel barrier Layer 180, 280, 380 Magnetization free layer 181, 281, 381 First magnetization fixed region 182, 282, 382 Second magnetization fixed region 183, 283 Magnetization region 184, 185 Notch 290 In-plane magnetization film

Claims (3)

A memory cell including a first magnetoresistive element whose resistance value switches between a first value and a second value;
A reference cell referred to for generating a reference level when reading data from the memory cell,
The reference cell includes a second magnetoresistive element having a resistance value fixed to a third value between the first value and the second value,
The first magnetoresistive element is:
A first magnetization fixed layer having perpendicular magnetic anisotropy and having a fixed magnetization direction;
A first magnetization free layer having at least a magnetization switching region having perpendicular magnetic anisotropy and having a magnetization direction parallel or antiparallel to the magnetization direction of the first magnetization fixed layer;
The first magnetization fixed layer and a first nonmagnetic layer sandwiched between the magnetization switching regions;
The second magnetoresistive element is
A second magnetization free layer having at least a magnetization region having perpendicular magnetic anisotropy and having a magnetization direction in the first direction;
A second magnetization fixed layer having perpendicular magnetic anisotropy and having a magnetization direction fixed in a second direction orthogonal to the first direction;
The second magnetization fixed layer and a second nonmagnetic layer sandwiched between the magnetization regions;
Either one of the first direction and the second direction is an in-plane direction , and the other is a vertical direction,
The second magnetoresistive element is
An in-plane magnetization film provided adjacent to one of the magnetization region and the second magnetization fixed layer that is magnetized in the in-plane direction.
Further comprising
The in-plane magnetization film is
Ferromagnetic or antiferromagnetic film with in-plane magnetic anisotropy
A magnetic random access memory comprising: The magnetic random access memory according to claim 1,
The first direction is an in-plane direction;
The in-plane magnetization film is a magnetic random access memory adjacent to the magnetization region of the second magnetization free layer . The magnetic random access memory according to claim 1,
The second direction is an in-plane direction;
The in-plane magnetization film is a magnetic random access memory adjacent to the second magnetization fixed layer .

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